New strategy for the construction of a monotetrahydrofuran ring in annonaceous acetogenin based on a ruthenium ring-closing metathesis:: Application to the synthesis of Solamin

An original convergent total synthesis of Solamin (type A annonaceous acetogenin) was achieved. The central THF core was obtained by means of a ring-closing metathesis (RCM) reaction using a ruthenium imidazolylidene complex. The RCM substrate was prepared from a vinyl-substituted epoxide by reaction with an allyl alcohol, both synthesized from propargylic alcohol. The flexibility of the strategy should be useful in preparing various natural and unnatural annonaceous acetogenins.